Loud, high-fidelity sound is desirable from speakers. This is easily achievable with large speakers. However, mobile devices are shrinking in size, and particularly in thickness. As the mobile device shrinks, the speaker must also shrink to accommodate the mobile form factor. A common speaker for mobile devices is a microspeaker. Regardless of the speaker choice, the reduced size can result in reduced quality of sound from mobile devices. Loud sounds require the cone of the microspeaker to extend further. However, the limited dimensions can cause the cone to contact a solid surface of the mobile device. Even small over-excursions can introduce very unpleasant audio artifacts. If over-excursion occurs for a prolonged time or is large in magnitude, the diaphragm can be mechanically damaged. A conventional solution for reducing such damage is the use of a speaker protection algorithm. The goal of a speaker protection algorithm is to protect the speaker from damage, while maximizing loudness and minimizing loss of audio quality. One conventional speaker protection technique is shown in FIG. 1.
FIG. 1 is a block diagram illustrating a conventional speaker protection system according to the prior art. An audio signal may be input to an adaptive excursion model 110, which generates an excursion prediction. This prediction is provided to an excursion limiter 104, which monitors the prediction for over-excursion events. When an over-excursion event is detected, the volume is rapidly decreased in proportion to the amount of predicted over-excursion. The excursion limiter 104 attenuates a delayed audio stream from delay block 102 to identify over-excursion events before they happen. The attenuated, delayed audio signal is then streamed to an audio amplifier 106, which generates the voltage signal for driving the speaker 112.
The excursion transfer function of the speaker, which is modeled by adaptive excursion model 110, may be subject to sources of variation including part-to-part variation from manufacturing, thermal variation, aging, wear, etc. The adaptive excursion model 110 adapts to these variations to estimate the current excursion transfer function for the speaker. A model adaptation block 108 uses a monitored current and voltage of the speaker to update the adaptive excursion model 110. For the adaptive modeling scheme to work, the model must be sufficiently complex to be able to capture all feasible types of model variation. Conventional solutions to improve the adaptive excursion model are to use higher order models. The drawback is that these higher order models have increased computational complexity that results in higher power usage. Power consumption in a mobile device results in shorter battery life. Also, the danger of over-parameterized models exists which can lead to more error and slower speed of convergence, further increasing power consumption and shortening battery life.
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved electrical components, particularly for audio systems employed in consumer-level devices, such as mobile phones. Embodiments described herein address certain shortcomings but not necessarily each and every one described here or known in the art. Furthermore, embodiments described herein may present other benefits than, and be used in other applications than, those of the shortcomings described above.